Sabot projectile



Patented Feb. 23, 1954 UNITED STATES PATENT OFFICE SABOT PROJECTILE Delaware 7 Application January 5, 1946, Serial No. 639,174

4 Claims.

This invention relates to an improvement in projectiles and more particularly to high velocity projectiles adapted for the penetration of ,armored structures.

Since the earliest use of iron clad naval craft and particularly since the more recent introduction of armored military land vehicles whose Weight and gun carrying capacity are limited by demands for maneuverability, there has been a constant struggle for superiority between the makers of armor plate and the makers of armor piercing ammunition. Each improvement in the ballistic strength of the armor plate or increase in the thickness of armor carried has brought about an increase in effectiveness of the ammunition expected to be used against such plate. Likewise, each improvement in the effectiveness of the projectile has usually been countered by a succeeding improvement in the armor plate.

This invention follows the present trend of the cycle and its primary objects are to effect a major improvement in the penetrative effectivenessof armor piercing ammunition and to, at the same time, effect a great improvement in the accuracy with which such fire may be delivered.

It is a further object to produce an effective subcaliber projectile which may be utilized without damage to the gun or parts thereof such as the muzzle brake. 7

An additional object is to furnish a projectile which may be economically and conveniently manufactured and assembled with a minimum of machine work necessary on diflicultly machineable components.

The invention contemplates accomplishing these objects by the use of a subcaliber projectile including a very hard and high density core, of substantially less than bore diameter, assembled in combination with a sabot of substantially bore diameter, the combination having materially less weight than the standard full caliber round. The sabot performs the functions of sealing the bore of the arm, imparting rotation to the subcaliber projectile, and guiding the same during its travel in the bore of the arm. During the combustion of the propellent charge, the sabot projectile receives from the charge substantially the same amount of energy as would normally be imparted to a standard full caliber round of approximately twice as great weight. As a result of this light weight, the velocity is much higher than that of a standard round, although little or no greater chamber pressure has been required.

Upon emergence of the sabot subcaliber projectile combination from the barrel of the gun, separation takes place and the subcaliber projecmg, in which:

tile which offers relatively small area to air resistance and is designed for high ballistic efliciency continues on its flight alone. The subcaliber projectile, in proportion to its physical dimensions, is very heavy and the major part of the kinetic energy imparted to the assembly is effective in maintaining the velocity thereof. By reason of its small physical dimensions, its retardation is comparatively low and its remaining Velocity on impact is materially greater than that of standard rounds. The sabot having a conformation unsuited for exterior ballistic efficiency decelerates and falls to the ground.

It is appreciated that this same general approach to the problem has been previously tried but the projectiles of the prior art suffered greatly from the lack of accuracy. Their design limitations were also such that they were apt to break up or become disassembled as they passed through the bore or else they would fail to separate at all. The problem may be better appreciated if it is realized that the sabot is given a strong impetus forward on the initiation of combustion in the propellent charge, and that as the rifiing bands of the sabot seat firmly in the rifling, the sabot itself is rather violently decelerated and the subcaliber projectile tends to continue without the sabot. As soon as the pressure has built up sufficiently to overcome the resistance of the rifiing, the sabot is again violently accelerated and, if there has been any separation, overtakes the subcaliber projectile with a severe impact apt to shatter the base of the sabot. The difliculty of preventing smash-ups in the bore without impeding the instant separation of the parts on emergence therefrom has been a serious one.

Another serious problem has arisen in connection with previous projectiles of this general type in that the sabot was apt to develop and transmit to the subcaliber projectile yawing tendencies too great to be cancelled out by the gymtory action of the spinning core. Akin to this defect has been one which may arise outside the bore when the sabot may yaw at the instant of separation and divert the axis of the spinning subcaliber projectile. Any such yawing force applied to the subcaliber projectile results in the development of gyratory precession and seriously disturbs the true flight of the projectile. As will appear more fully hereafter, this invention presents a practical solution to both of the problems mentioned. I

The exact nature of the invention as well as other ob ects and advantages "thereof will be readily apparent from consideration of the drawence, it may be seen that the invention comprises two major units, of which the first .to described is the subcaliber projectile. The :principal part of this subcaliber projectile is an extremely hard and high densitypenetrating-eore "l A preferred material for this core is tungsten w carbide, which may be sintered in the well-known manner with cobalt or some other suitableme'tal. Suitable proportions are from 87% to 90% .tungsten carbide and 10% to 13% cobalt. It will, of course, be realized that the principles of this invention are equally applicable to "oth er choices of material for the penetrating "core.

The difficulty of machining the ma-terials suitable for use as penetrating cores is'well'known and for mass production it has been a practical necessity that the'contours of the core be hept to the simplest form consistent with accomplishing theirintended purpose. Tungstencarbideisnormally molded into bars 'from powder form, machined to size, and sintered, after which further machining operationscan only be carried out by the expensive process of grinding with diamond wheels. In order to permit the utilization of simple'shapes and'to'allow the otherrequirements to be met without requiring grinding of the heat treated .core to extremely precise 'radial dimensions'there has been provided:anenclosing sheath 2 of steel or other suitable, easily'machineable material which engages the core and provides f'or its secure attachment to and ready release from the sabot to be later described in detail.

The sheath has an internal :diameter slightly larger than may be expected-of the 'largest unground core which will-come withinspeoification tolerances inlregardto diameter, eccentricity,'and the like. A suitable *method'of insuring that the core is adequately and concentrically joined to the sheath is to insert the core into thes'heath and space it in'centered relation theretoby theiinsertion at 120 intervals of three identical wires of the largest diameter'that may beforced into-the cap 4 'of'Duralumin or other'lightmetal enclosing the nose of the .core I. .This nose 'cap has the usual functions of improving ballistic efiiciency by its streamlining effect and on impact aidspenetration byfurnishing lateral suppontand lubrication to thepoint .of the core.

The second major unit, or the sabot,.is=built--.up from the cup dike body 5 which-is pr-ovidedonats front and rear outer cylindrical surfaces with carefully machined-bearing-areasi-B. aThese bearing areas are adapted to ride on theismfaoe of the lands of the rifiing without being engraved as the projectile passes through the barrel. The function of imparting rotation to the subcaliber projectile by engagement with the rifiing is performeda'byitherotating bands '"I which are seated in-suitable grooves in the sabot body preferably somewhat to the rear of the center of gravity of "the assembled sabot-subcaliber combination.

At .least one of the rotating bands is formed with a portion of diameter great enough to engage the wall'oflthe chamber in the rear of the forcing cone and insure that the sabot will be centered in the boreinspit-e of possible irregularities in thethicknessor alignment of a cartridge case in the chamber. This feature requires that the band be capable of withstanding an augmented :radialrcompression without damage to the riiling. It has been found that a porous sintered iron rotating band is admirably suited to this purpose since it compresses radially without any tendency to *flowback and simply becomes'more dense in the region immediate'lyin contact with the rifling. Although the shearstrength per unit area of sintered iron is not as great as that'of somepreviously used materials, its ready compressibility enables large areas to be used without overloading-the rifiing. The melting point of the sintered iron band is"higher and its coefficient of friction under'working"conditionsappears to beless than that of the other conventional materials. Such bands do 'not, therefore, wear off :or become subject to-local'fus'ion where theypontact the rifling. The action of this material is also more uniform and less'subject to uneven deformation than that of some solid materials. Preferably such bands are impregnated with paraffin or other suitable lubricant which -"has the dual function of rustproofing the band and lubricating the bore. The effectiveness of such bands is evident from an inspection of 'sabots Jfired for recovery. The engraving .of'the bands is clean .cut .and uniform, whereas 'when the bands are of other materials theban'ds themselves "show wide, ragged grooves of'muchgreater extent than required for the pas sage of .the lands of the rifiing.

To decrease the weight of the sabot, approximately its'frontlhalf may beperforated with holes such'asth'ose shown at '8.

The basal portion 9 of the cup-shaped sabot provides a rearwardly and inwardly extending flange whose function will be more fully discussed hereinafter. .Ihe retaining flange may be intogral with the sabot or may comprise a retaining washer .l I secured thereto as by screws it.

Cemented to the rear face of the retaining washer is .an obturator cup or ,gas check [2 which may be formed of rubber, neoprene, or other plastic rubberlike material. The flared skirt of such .an obturator receives the pressure of the propellentgases and'functions asan efiectiveseal to ,prevent the possibility of non-uniform application .of gas ,pressure in .the annular space in therearof therotating bands. Theeffectiveness of .this.obturator mayalso be determined by the F inspection of .the bodies of sabots fired for recovery. Unless such an obturator is used, the sabot body will be deeply .scored or engraved, showing that there has ,been .a non-uniform pressure application tending to cant .the assembly in the barrel.

-A bearing band .43 maybe formed integrally with rthewsabot body, tor for lightness in weight and convenience inmachiningmay be of Duralumin or iother suitable light metal received in the cuplike sabot :body and secured thereto with 5 the inner face of the bearing band concentrically disposed with relation to the axis of the cup. To insure absolute accuracy, if the bearing band is a separate element, it is preferable that the bearing band l3 be shrunk into its seat and ground to a perfect fit with the sheath. It may be further retained by the use of set screws such as those shown at M. The base 9 of the cup 5 is centrally apertured at l5 to receive with a very accurate fit the rearward extension it formed on the base of the core sheath 2, and carefully machined mating flat surfaces are provided on the rear face I! of the sheath and on the forwardly facing inner surface l8 of the base of the body. The extension may conveniently be formed to include a tracer cavity Hill. The outer surfaces of the sheath and nose cap are spaced a considerable distance radially inward from the inner surface of the front portion of the body, and the sheath is diametrically reduced at I9 in the region to the rear of the bearing band. This clearance has an important bearing on the accuracy, with which the subcaliber projectile separates from the sabot and will be discussed in more detail hereafter.

The rearward extension on the sheath isprovided with a circumferential groove 20 in the region immediately behind the rearward face 2i of the base of the sabot body. Half-circular re taining shoes 22 (see Fig. 4) are adapted to encircle the rearward extension and are provided with inner surfaces adapted to be engaged in the groove in the rearward extension in such fashion as to provide a wedge-like action between the forwardly facing rear wall of the groove and the rearwardly facing base of the body. These seg- 1 ments or retaining shoes are secured in the groove by having retaining springs 23 engaged about their outer circumference. Each of the springs (see Fig. 3) is preferably in the form of a substantially complete circle and the springs are adapted under the action of centrifugal force to expand to a degree suflicient to permit the retaining shoes to disengage themselves from the groove.

To insure that the springs and retaining shoes by centrifugal force until after the sabot has cleared the muzzle brake.

In use, this projectile may be loaded into a gun and fired in the usual manner, either as an element of fixed or separate loading ammunition. Upon firing of the propellent charge, the sabot receives a forward impetus of considerable magnitude, and by reason of the inter-engagement between the sheath and the'sabot body, this forward impetus is communicated to the subcaliber projectile assembly. The retaining shoes 22 and springs 23 adequately resist the tendency (heretofore noted) of the projectile to separate from the sabot when the latter is retarded by its initial engagement with the rifling. During the period in which this tendency toward separation is likely to be active, the combined pro-' ,jectile assembly will not have acquired asigniflcant rotational velocity. Thus, the full shearing area of the retaining shoe ribs'is available to resist such separation during the period when it is needed the most. As the projectile assembly moves through the gun barrel, there will be suflicient acceleration of theassembly to insure that the forces of inertia maintain high pressures at the contacting face between the subcaliber sheath and the base of the sabot. This engagement functions in the manner of a friction clutch to transmit to the'sheath and therefore to the core of the subcaliber projectile the rotating force applied to the sabot by the inter-engagement of the bands and the rifling. The centrifugal force generated by rotation as the projectile moves through the bore overcomes the resistance of the spring rings and allows the segments of the retaining shoes to become disengaged from the extension on the rear of the sheath. The retaining flange provides a compartment in which the springs and retaining shoes are received and held by the continued action of centrifugal force. It is of considerable importance that the retaining flange function in this manner for otherwise retaining shoes and springs would be at liberty to contact the walls of the bore with possible injury to them and would almost certainly do severe damage to the muzzle brake.

During the passage of the projectile assembly through the bore, the gas check functions in a manner similar to that of the Well-known cup pump leather and completely seals the bore against any penetration of gas through the annular space surrounding the sabot body. This has the effect of protecting both the bore and the rifling bands from the effects of gas erosion, which are severe when any leakage is permitted, as well" as insuring the uniformity of pressure application previously mentioned. While it may seem that there would be a tendency for gas pressure to force the subcaliber projectile forwardly from its seat in the sabot, it should be borne in mind that the subcaliber projectile is largely composed of very high density material. Since the whole assembly is accelerating at a very high rate as it passes through the bore, the normal forces of inertia will hold the subcaliber projec-' tile on its ground seat with sufficient bearing pressure to overcome the possibility of any leakage or slippage due to rotary acceleration.

When the projectile assembly leaves the muzzle of the gun, air resistance acting on the sabot will cause it to decelerate rapidly. The subcaliber projectile presents amuch smaller body and one which is properly shaped for minimum air resistance. It will be seen, therefore, that the subcaliber projectile will separate at once from the sabot. It was previously pointed out that there is a considerable clearance between the forward portion of the sabot and the projectile sheath and that the rearward portion of the sheath was reduced in diameter immediately behind the bearing ring. Thus, as soon as there has been any appreciable relative axial movement between the sabot and the subcaliber projectile, the projectile will be substantially, free, from. any forces that might be exerted by the sabot. If, for; example, the sabot tended .to yaw in the process of separation, it would be impossible for this force to be transmitted to the subcaliber pro-. jectile in such manner as to disturb its true; flight. The fact that the sabot is provided with widely spaced bearing areas at its end portions} that it is thoroughly obturated and that the rifling bands are true and of ample strength, insures that, the sabot and subcaliber assembly will'have been; delivered from the muzzle. 'of the gun without;- initial yaw. The axial separation :necessary to;

1; rtire subcaliber projectile stakes ijplace :inthe first iiew feet :of ireezfiightmnd during :this short interval the asabiot '-.-Wi11 mot :have ran :opportunity to develop on tho transmit to athe subcaliber ,projectileryawingitendencies havingianzadverseeifect on;accuraoy.

'A'fter separation of the subcaliber projectile from the rebut, the latter which presents a very poor ballistic contour, will :rapidly ,decelerate and fall :to 'the ground. 7131c :subcaliber projectile will continue sby itself :at an extremely high velocity and zon impact :with the target the nose cap will perform the usualfunction of lubricating and supporting the point of ithe penetrating core. Ll-The penetrating -coreiis, as has .been previously moted, of very 'high density, and being composed largely .of -.one of the hardest known materials is well adapted for :the :penetration of armor. As the ".cOl'e penetrates, the sheath will probably be stripped off, but since its mass is insignificant incomparison-with thatrof the core itself ,'the v loss'of the momentum of ;the sheath will not exert an appreciable .effect upon the penetrative efiectiveness of the .core.

We claim:

.1. In a sabot projectile for rifiedtguns comprising anassemblyofasabot with a subcaliber projectile; -.the .combination including a sabot having an axially ,apertured base, flanged means on the sabot ;provided .with a central opening and defining an annular recess surrounding and extending rearwardly from :the rear opening of the apertured base, asubcaliber projectile sengaging the :sabot vand having .an axial rearward extension provided with a tracer cavity reaching through the aperture in thesabot base, an annular groove in the extension; and centrifugally releasableretaining means comprising segmental retaining shoes en a ed between .the annular groove and the sabot base, .and .a plurality of spring rings embracing theshoes, the said recess providingianannularrcompartmentifor the receptionrandcarrying of the releasable means when their releaseihasbeenleflected by rotation of the assembly, whileallowing said tracer cavity to be I rearwardly'exposedthrough said central. opening.

2. In (asabot projectile for rifled guns comprising an assembly ,ofa sabot with a subcaliber projectile; .the combination including a sabot comprising .a :generally cylindrical deep cupshaped member .havinglan open forward end and a scentrallyrdisposed aperture in the base .thereof, .spaced bearing surfaces on the exterior of thesabot adapted'to slide on theisurface of the lands of-a rifled gun, rotatingband meanslocated between the .spaced "bearing surfaces, a rearwardly and inwardly extending flange on the base of the sabot provided with a substantially axially disposed opening and defining ,an anmilar recess surrounding and extending rear wardly from the rear opening of the aperture inithe base, a supporting band within the sabot spaced rearwardlyfirom the open end thereof by not substantiallyless than one-half the depth thereof and having therein an opening coaxial with "the exterior bearing surfaces and with the aperture .in the "base; 'a subcaliber projectile of substantially .less maximum diameter than the inside diameter of the sabot forward of said supporting band comprising a generally cylindrical portion received within the supporting band,abase in engagement with the base of the sabot, 'an extension on' the base of the subcaliber projectile -=reaching "through tl'ie aperture in the base of thevsabotl-sandipmvided :with a' tracer cavity exposed to said :axially disposed opening,

81 an ramiular :groove in ithe sextension; rand xentrifugally releasablezretaining rmeans within-said annular recess comprising retaining shoes engaged between the annular groove and the base of the :sabot, and "spring :means releasably encircling the retaining :shoes.

3. in a :sabot projectile for rifled guns .comprising fan assemblyofasabot with a-subcaliber projectile; the -.combination including a sabot comprising .a rgenerally cylindrical deep cupshaped. member having an open forward end and a centrally idisposed'aperture in-thebase thereof, longitudinally spaced bearing surfaces on the exterior of the sabot adapted .to slide on the surfaceofrthelands of arifled gun, rotatingband means located on the exterior of .thersabot .between thebearing surfaces, a foremost internal supporting band within the sabot spaced rearwardly from the open end thereof by notsubstantially less than one-half the depth thereof, said supporting iband having therein an opening coaxial with the exterior bearing surface and with the apertureiin the base; a subcaliber projectile of substantially less maximum diameter than the inside diameter of said sabot forward of .said supporting band comprising a generally cylindricalportion received within the supporting band, a base in engagement with vthe'baseoff the sabot, an extension ontheibase of the subcaliber projectile reaching through the aperture in the base of the sabot, the diameter of the body of the subcaliber projectile in "the rear of the supporting band being ,so reduced that after slight axial separation there is freedom for relative inclination between the axis of :the subcaliber projectile and the axis of the sabot; and centrifugally-releasable means for securing the subcaliber projectile'in the sabot until the assembly has attained a predeterminedrotational velocity, said releasable meanscomprising separable shoes inter-engaged between the rearmost face of the base of said sabot and the portion of said extension reaching entirely through said aperture in the'base of the "sabot.

4. In a sabot projectile for rifled guns comprising an assembly of a sabot with a subcaliber projectile; the combination including a sabot comprising a generally cylindrical deep cupshaped member'having an open "forward end and a centrally disposed aperture-inthe base thereof, longitudinally spaced bearing surfaces on the exterior :of the sabot adapted to slide on the surface of the lands of a rifled gun, rotating band means located .on ithe exterior of the sabotbetween the "bearing surfaces, a foremost internal supporting band within the sabot spaced rearwardly from the open end thereof by not substantially less than one-half the depth thereof, said :band :having xtherein an opening 'of greater diameter than the aperture in the base coaxial with the exterior rbearing surf aces and with said aperture; 12. subcaliber proj ectile of substantially less maximum diameter than the inside diameter of the ssabot :forward :of said supporting band comprising a generally cylindrical portion received within the supportingband, the subcaliber projectile being reduced inwdiameter behind the supporting band, a flat-base inengagement with the base :of the sabot, ,an'extension on the-subcaliber projectile-engaged withthe aperture in thebasgofthesabot'and extending therethrough; and centrifugally releasable means for securing the subcaliber projectile %in the sabot until the assembly has attaineda predetermined rotational velocity; said releasablemeanstcomprising separable rshoes iinter engaged between the 'rearmost face of the base of said sabot and the portion of said extension extending entirely through said aperture, and spring means releasably encircling said shoes.

PAUL F. DARBY.

THOMAS R. KINRAIDE.

ROBERT A. A. HENTSCHEL.

JOHN HAMMOND.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 36,879 Bird Nov. 4, 1862 41,127 Smith Jan. 5, 1864 1,380,774 Clay et a1. June 7, 1921 Number Number Name Dat Dougan Sept. 12, 1922 Calkins Oct. 17, 1944 Martin Jan. 29, 1946 Patch et a1 Oct. 15, 1946 FOREIGN PATENTS Country Date Great Britain Feb. 1, 1883 Great Britain July 23, 1898 Sweden Nov. 5, 1919 France July 27, 1936 France Feb. 8, 1937 

